This invention relates to a radar system for use especially with aircraft, and capable of automatic horizontal and vertical scanning and display of radar signals for presentation of a selectable vertical range for both a plan view and vertical view, and with the plan view display being with reference to latitude and longitude, if desired.
Conventional airborne weather radar systems display radar returns in a plan view only, representing weather images as the radar beam sweeps horizontally back and forth ahead of the aircraft, although a proposal for automatically displaying radar returns in both plan view and vertical view has been disclosed in U.S. Pat. No. 4,940,987. With the system of the patent, more information is available to the user since height, as well as horizontal extent, of weather conditions can be determined whereas, with the conventional systems, only the horizontal extent can be ascertained (at least automatically) Of course, knowing the height of a weather condition would enable the user of the system to determine whether flying above the condition were possible or whether flying around the system would be necessary.
Prior to the system of the afore-cited patent, determination of height of weather conditions had to be made by manually tilting the radar antenna up or down so that radar returns could be taken along sweeps at different elevations. Then, knowing the angle of elevation of the radar beam, the altitude of the aircraft, and the distance of certain echo returns, a trigonometric calculation or estimate could be made as to the height or elevation of weather conditions from which the echoes were reflected. Such manual tilting and elevation calculation, however, were time consuming, and a flight crew typically would not have the time to perform such operations, especially when flying in a stormy weather condition. Of course, with the system of the patent, such manual tilting and calculation is obviated.
Oftentimes during flight, the pilot will have no need for display of weather or other echo causing conditions much below the altitude of the aircraft, and yet such conditions may nevertheless be displayed on conventional weather radar systems (unless the pilot manually sets the radar antenna above a certain level). It would be desirable to eliminate such distracting echoes, such as ground clutter (echoes from terrain) which are sometimes not easy to distinguish from storms particularly in mountainous regions, to reduce the likelihood of pilot or navigator confusion.
Besides more accurate information on weather conditions now being available to pilots, so-called moving map displays have recently become available. With these displays, the positions of airports, navigational stations and airway intersections are provided in data bases for display in aircraft cockpits. Typically, symbols representing these positions are superimposed on weather radar displays as well as other display devices on the instrument panel. With real-time radar, such moving map displays are useful primarily when the aircraft course is constant and the aircraft speed is not great relative to the sweep cycle time of the radar antenna. However, when the aircraft turns or changes altitude, the display may be smeared until a new steady course is established. Further, with raster scanning radar systems, the overall scan cycle is much longer than with single sweep scan radars and thus the returns will be out of register relative to those of subsequent and prior cycles. In U.S. Pat. No. 5,049,886, a system is described which seeks to mitigate this problem by storing data referenced to the aircraft and then using heading and speed information to correct the display for aircraft motion. However, the system corrects the plan view only for translation and heading changes.